foundation-sites: replaced.zf.interchange JS event not fired for background images

If you check the code here, you can see that the replaced event is never fired if Interchange is changing background images. I know that you can’t hook on the “completed” change of background-image, so technically the event will fire earlier than the other two cases, but I really need that JS event, and it worked in F5.

Thanks for the hard work on F6!